Power supply apparatus and method for wireless power transmission

ABSTRACT

Provided is an apparatus and method that may stably perform wireless transmission. According to one general aspect, a power supply for a wireless power transmitter may include: a detecting unit configured to detect voltage, current, or both supplied to a power amplifier (PA); a controller configured to determine power supplied to the PA based on the detected voltage, the detected current, or both, and to determine a reference current based on the determined power supplied to the PA; and a breaker configured to cut off the power supplied to the PA based on a comparison of current supplied to the PA and the reference current.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2011-0053190, filed on Jun. 2, 2011, in theKorean Intellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND

1. Field

The following description relates to wireless power transmission.

2. Description of Related Art

As demand for portable electronic devices has rapidly increased, use ofwired power supplies for these devices has become more inconvenient.Studies on wireless power transmission have been conducted to overcomeinconveniences of wired power supplies and the limited capacity ofconventional batteries. One conventional wireless power transmissiontechnology uses a resonance characteristic of a radio frequency (RF)device that may include a source that supplies power and a target thatreceives power.

SUMMARY

According to one general aspect, a power supply for a wireless powertransmitter may include: a detecting unit configured to detect voltage,current, or both supplied to a power amplifier (PA); a controllerconfigured to determine power supplied to the PA based on the detectedvoltage, the detected current, or both, and to determine a referencecurrent based on the determined power supplied to the PA; and a breakerconfigured to cut off the power supplied to the PA based on a comparisonof current supplied to the PA and the reference current.

The detecting unit may measure voltage across a resistor or a transistorconnected to the PA, measures current flowing through the resistor orthe transistor, or both.

The detecting unit may measure voltage across a resistor having apredetermined resistance connected to the PA, and determines the currentbased on the predetermined resistance and the measured voltage.

The controller may determine the reference current using a referencetable in which reference currents, predetermined supply powers, andsupply voltages, are provided.

The controller may control a signal input to the PA based on thecomparison.

The controller may control power output from a power converter thatprovides supply power to the PA based on the comparison.

The power supply may further include: a comparing unit configured tocompare the detected current and the reference current.

The breaker may determine the state of a switch that connects the PA anda power converter based on the comparison.

The breaker may determine an operation of a transistor that connects thePA and a power converter based on the comparison.

The power supply may further include: a leakage current breakerconfigured to cut off a leakage current.

The power supply may further include: a source resonance unit configuredto transmit power output from the PA; and a matching network configuredto match an output impedance of the PA and an input impedance of thesource resonator.

According to another general aspect, a power supply method for wirelesspower transmission may include: detecting voltage, current, or both,supplied to a power amplifier (PA); determining power supplied to the PAbased on the detected voltage, the detected current, or both;determining a reference current based on the determined power suppliedto the PA; and cutting off the power supplied to the PA based on acomparison between current supplied to the PA and the reference current.

The detecting may include: measuring voltage across a resistor or atransistor connected to the PA, measuring current flowing through theresistor or the transistor, or both.

The detecting may include: measuring voltage across a resistor having apredetermined resistance connected to the PA; and determining thecurrent based on the predetermined resistance and the measured voltage.

The method may further include: controlling power output from a powerconverter that provides power to the PA based on the comparison.

The method may further include: comparing the detected current and thereference current.

The cutting off may include: cutting off an electrical connectionbetween the PA and the power converter based on the comparison.

According to yet another general aspect, a wireless power transmittermay include the aforementioned power supply.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a wireless power transmission system.

FIG. 2 is a block diagram illustrating a wireless power transmitter.

FIG. 3 is a diagram illustrating a wireless power transmitter.

FIG. 4 is a diagram illustrating a wireless power transmitter.

FIG. 5 is a graph illustrating stable ranges of current supplied to onepower amplifier (PA).

FIG. 6 is a diagram illustrating a reference table.

FIGS. 7A and 7B are diagrams illustrating a distribution of a magneticfield in a feeder and a source resonator.

FIGS. 8A and 8B are diagrams illustrating a wireless power transmitter.

FIG. 9A is a diagram illustrating a distribution of a magnetic fieldwithin a source resonator based on feeding of a feeding unit.

FIG. 9B is a diagram illustrating equivalent circuits of a feeding unitand a source resonator.

FIG. 10 illustrates an electric vehicle charging system.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals should be understood torefer to the same elements, features, and structures. The relative sizesand depictions of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses and/orsystems described herein. Accordingly, various changes, modifications,and equivalents of the systems, apparatuses and/or methods describedherein may be suggested to those of ordinary skill in the art. Theprogression of processing steps and/or operations described is anexample; however, the sequence of and/or operations is not limited tothat set forth herein and may be changed as is known in the art, withthe exception of steps and/or operations necessarily occurring in acertain order. Also, descriptions of well-known functions andconstructions may be omitted for increased clarity and conciseness.

FIG. 1 illustrates a wireless power transmission system.

Referring to FIG. 1, the wireless power transmission system includes asource device 110 and a target device 120. The source device 110 maycorrespond to a device supplying wireless power and may include variouselectric devices that supply power, such as pads, terminals, televisions(TVs), and the like. The target device 120 may correspond to a devicereceiving wireless power, and may include an assorted range ofelectronic devices that consume power, such as terminals, TVs, vehicles,washing machines, radios, lights and the like.

The source device 110 may include an alternating current-to-directcurrent (AC/DC) converter 111, a power detector 113, a power converter114, a control/communication unit 115, and a source resonator 116.

The target device 120 may include a target resonator 121, arectification unit 122, a DC-to-DC (DC/DC) converter 123, a switch unit124, a charging unit 125, and a control/communication unit 126.

The AC/DC converter 111 may generate DC voltage by converting AC voltageoutput from a power supply 112. The AC/DC converter 111 may output DCvoltage of a predetermined level, and/or may adjust an output level ofDC voltage based on the control of the control/communication unit 115.

The power detector 113 may detect current, voltage, or both, output fromthe AC/DC converter 111, and may transfer, to the control/communicationunit 115, information on the detected current and the detected voltage.Also, the power detector 113 may detect current, voltage, or both inputto the power converter 114.

The power converter 114 may generate power by converting DC voltage of apredetermined level to AC voltage, for example, using a switching pulsesignal in a band of a few megahertz (MHz) to tens of MHz. The powerconverter 114 may convert the DC voltage to the AC voltage using aresonance frequency and thus, may generate communication power to beused for communication or charging power to be used for charging used inthe target device 120. The communication power to be used forcommunication may correspond to energy for activating a processor and acommunication module of the target device 120 and may be referred to asa wake-up power in terms of the energy for activating the processor andthe communication module of the target device 120. For example, thecommunication power to be used for communication may be transmitted in aform of a constant wave during a predetermined time. The charging powerto be used for charging may correspond to energy for charging a batteryconnected to or included in the target device 120. Moreover, thecharging power may be continuously transmitted during a predeterminedtime, and may be transmitted at a power level greater than thecommunication power to be used for communication.

The control/communication unit 115 may control the frequency of aswitching pulse signal. The frequency of the switching pulse signal maybe determined based on the control of the control/communication unit115. By controlling the power converter 114, the control/communicationunit 115 may generate a modulated signal to be transmitted to the targetdevice 120. The control/communication unit 115 may transmit variousmessages to the target device 120, through in-band communication. Thein-band communication may denote communication performed using the samefrequency as a resonance frequency used for wireless power transmission.The control/communication unit 115 may detect a reflected wave, and maydemodulate a signal received from the target device 120 through anenvelope of the detected reflected wave.

The control/communication unit 115 may generate a modulated signal forin-band communication, using various schemes. To generate the modulatedsignal, the control/communication unit 115 may turn a switching pulsesignal ON and OFF, and/or may perform delta-sigma modulation.Additionally, the control/communication unit 115 may generate apulse-width modulated (PWM) signal having a predetermined envelope.

The control/communication unit 115 may perform out-band communicationusing a communication channel, as opposed to using the resonancefrequency. The control/communication unit 115 may include acommunication module, such as one configured to process ZigBee,Bluetooth, Wi-Fi, or Wi-Max communications and the like. Thecontrol/communication unit 115 may perform transmission and reception ofdata with the target device 120, through out-band communication.

The term “in-band” communication(s), as used herein, meanscommunication(s) in which information (such as, for example, controlinformation, data and/or metadata) is transmitted in the same frequencyband, and/or on the same channel, as used for power transmission.According to one or more embodiments, the frequency may be a resonancefrequency. And, the term “out-band” communication(s), as used herein,means communication(s) in which information (such as, for example,control information, data and/or metadata) is transmitted in a separatefrequency band and/or using a separate or dedicated channel, than usedfor power transmission.

The source resonator 116 may transfer electromagnetic energy to thetarget resonator 121. For instance, the source resonator 116 maytransfer, to the target device 120, a communication power to be used forcommunication or a charging power to be used for charging throughmagnetic coupling with the target resonator 121.

The target resonator 121 may receive the electromagnetic energy from thesource resonator 116. The target resonator 121 may receive, from thesource device 110, the communication power to be used for communicationor the charging power to be used for charging through magnetic couplingwith the source resonator 116. The target resonator 121 may receivevarious messages from the source device 110 through in-bandcommunication.

The rectifying unit 122 may generate DC voltage by rectifying AC voltagereceived by the target resonator 121.

The DC/DC converter 123 may adjust a level of the DC voltage output fromthe rectifying unit 122 based on a capacity of the charging unit 125.For example, the DC/DC converter 123 may adjust, the level of the DCvoltage output from the rectifying unit 122 from 3 Volts (V) to 10 V.

The switch unit 124 may be actuated (e.g., turned ON and OFF) based onthe control of the control/communication unit 126. When the switch unit124 is turned OFF, the control/communication 115 of the source device110 may detect a reflected wave. Also, when the switch unit 124 isturned OFF, the magnetic coupling between the source resonator 116 andthe target resonator 121 may be eliminated.

The charging unit 125 may include at least one battery. The chargingunit 125 may be configured to charge the at least one battery using DCvoltage output from the DC/DC converter 123.

The control/communication unit 126 may perform in-band communication fortransmitting and receiving data using a resonance frequency. Forexample, the control/communication unit 126 may demodulate a receivedsignal by detecting a signal between the target resonator 121 and therectifying unit 122, or by detecting an output signal of the rectifyingunit 122. The control/communication unit 126 may demodulate a messagereceived through the in-band communication.

The control/communication unit 126 may adjust an impedance of the targetresonator 121 so as to modulate a signal to be transmitted to the sourcedevice 110. The control/communication unit 126 may modulate the signalto be transmitted to the source device 110, by turning the switch unit1240N and OFF. For example, the control/communication unit 126 mayincrease the impedance of the target resonator 121 so that a reflectedwave may be detected from the control/communication unit 115 of thesource device 110. Depending on whether the reflected wave is detected,the control/communication unit 115 may detect a binary number (e.g., “0”or “1”).

The control/communication unit 126 may perform out-band communicationusing a communication channel. The control/communication unit 126 mayinclude a communication module, such as one configured to processZigbee, Bluetooth, Wi-Fi or Wi-Max communications and the like. Thecontrol/communication 126 may perform transmission and reception of datawith the source device 110.

FIG. 2 illustrates a wireless power transmitter.

In some instance, a load of a target device changes an output power of apower amplifier (PA) may momentarily be out of a stable output range.The stable output range may be a range in which the PA outputs powerwithout causing damage to the PA. Determining that the output power ofthe PA may be momentarily out of the stable output range, and adjustingthe output power to enter the stable output range would be beneficial.

Referring to FIG. 2, the wireless power transmitter includes a frequencygenerating unit 201, a PA 203, a matching network 205, a sourceresonance unit 207, a detecting unit 210, a controller 220, a breaker230, and a power converter 240.

The frequency generating unit 201 may be configured to generate theresonance frequency. The resonance frequency may be determined by acontroller 220. The controller 220 may perform impedance matchingbetween a source device and the target device, and may determine aresonance frequency. The power converter 240 may rectify an AC signalinput from an external side so as to convert the AC signal to apredetermined DC signal. The power converter 240 may adjust themagnitude of a DC signal based on control of the controller 220. Thepower converter 240 may increase the magnitude of the DC signal or maydecrease the magnitude of the DC signal based on the control of thecontroller 220. A DC signal output from the power converter 240 may beinput to the PA 203 as a supply power, for instance.

An output power of the PA 203 may change based on a load of the targetdevice. The PA 203 may generate an output power satisfying a requestedpower of the load of the target device. For example, the PA 203 mayamplify an input signal based on the supply power where the input signalmay be a resonance frequency signal. The supply power may be provided bythe power converter 240, based on control of the controller 220. In oneor more embodiments, the supply power of the PA 203 may be calculated bymeasuring a supply voltage, a supply current, or both.

The matching network 205 may match an input impedance shown in adirection from the matching network 205 to the target device and anoutput impedance of the PA 203. The matching network 205 may match aninput impedance of a source resonator and the output impedance of the PA203. The input impedance may change as the load of the target devicechanges.

The source resonance unit 207 may be configured to transmit power outputfrom the PA 203 through magnetic coupling between the source resonatorand a target resonator. Power may be wirelessly transmitted by anelectromagnetic wave propagated by the source resonator. For example,magnetic coupling may be performed based on a resonance frequencybetween the source resonator and the target resonator. When a relativelyhigh Q-factor exists between the source resonator and the targetresonator, the output power of the PA 203 may be effectively transferredto the target resonator.

The detecting unit 210 may be configured to detect the supply voltage orthe supply current of the PA 203. The supply power may be generated bythe power converter 240. In this example, the supply power may becalculated based on the supply voltage and the supply current. In someimplementations, the power converter 240 may be configured as aswitching mode power supply (SMPS). When the load of the target devicechanges, the controller 220 may control the matching network 205 tomatch the output impedance and the input impedance that vary due to thechange in the load of the target device. The controller 220 may controlthe output power of the PA 203 to satisfy the requested power level ofthe load of the target device. The output power of the PA 203 may bedetermined based on the supply power of the PA 203.

The detecting unit 210 may be configured to detect or measure a voltageacross a predetermined resistor connected between the power converter240 and the PA 203. The detecting unit 210 may determine the currentflowing through the predetermined resistor based on a value of thepredetermined resistor and the voltage between the both ends of thepredetermined resistor. The current flowing through the predeterminedresistor may be provided as the supply current of the PA 203. In someembodiments, the detecting unit 210 may directly detect the currentflowing through the predetermined resistor. For example, the detectingunit 210 may periodically or continuously detect or measure the voltagebetween the both ends of the predetermined resistor. The detecting unit210 may detect the voltage between the both ends of the predeterminedresistor for each determined time based on control of the controller220.

The detecting unit 210 may be configured to detect voltage between theboth ends of an ON resistor of a transistor connected between the powerconverter 240 and the PA 203. The detecting unit 210 may detect acurrent flowing through the ON resistor based on a resistance value ofthe ON resistor and the voltage between the both ends of the ONresistor. The current flowing through the ON resistor may be provided asthe supply current of the PA 203. The detecting unit 210 may directlydetect the current flowing through the ON resistor of the transistor.The detecting unit 210 may detect a voltage between both ends of a lineimpedance connected between the power converter 240 and the PA 203. Thedetecting unit 210 may detect current flowing through the line impedancebased on a value of the line impedance and the voltage between the bothends of the line impedance. The detecting unit 210 may directly detector measure the current flowing through the line impedance, in someinstances.

The controller 220 may be configured to calculate or determine thesupply power based on the supply voltage, the supply current, or both,detected by the detecting unit 210. The controller 220 may determine areference current based on the supply power and the detected supplyvoltage. The controller 220 may include a reference table. The referencetable may include reference currents matching predetermined supplypowers and predetermined supply voltages, in some embodiments.Therefore, the controller 220 may determine the reference current basedon the reference table, the calculated supply power, and the detectedsupply voltage. The reference current may denote a limiting currentindicating an operating limit of the PA 203. For example, when currentsupplied to the PA 203 is greater than the reference current, the PA 203may malfunction or may stop operating. The reference current may denotea limiting current having a predetermined margin from the operatinglimit of the PA 203. The controller 220 may determine the referencecurrent based on the supply power, the supply voltage, the supplycurrent data, or any combination thereof, that are statisticallycollected.

Whether the limiting current indicating the operating limit of the PA203 is set as the reference current or the limiting current having thepredetermined margin from the operating limit of the PA 203 is set asthe reference current may be determined in advance or may be changed bya user.

The controller 220 may control a switch 221 based on a comparison of thereference current and the supply current detected by the detecting unit210. The electrical connection between the frequency generating unit 201and the PA 203 may be controlled by turning ON and OFF the switch 221.For instance, the controller 220 may turn the switch 221 OFF when thedetected supply current is greater than the reference current. Theresonance frequency signal generated by the frequency generating unit201 may be an input to the PA 203. When the input signal is not input tothe PA 203, the PA 203 may not output power. The controller 220 may turnthe electrical connection between the frequency generating unit 201 andthe PA 203 OFF and thus, may prevent the PA 203 from generating anoutput power that momentarily exceeds the stable output range. Thecontroller 220 may turn the switch 2210N when the detected supplycurrent is less than or equal to the reference current.

The controller 220 may control the output power of the power converter240 based on a result of comparison between the detected supply currentand the reference current. The output power of the power converter 240may be provided as the supply power of the PA 203. When the detectedsupply current is greater than the reference current, the controller 220may control the power converter 240 to output an amount of power that isless than the existing output power.

Since the output power of the power converter 240 is decreased, the PA203 may generate an output power within the stable output range. Thecontroller 220 may control the power converter 240 to not output powerduring a predetermined time.

The breaker 230 may be configured to cut off an electrical connectionbetween the power converter 240 and the PA 203 based on a result ofcomparison between the supply current detected by the detecting unit 210and the reference current determined by the controller 220. When thedetected supply current is greater than the reference current, thecontroller 220 may control the breaker 230 to cut off the electricalconnection between the power converter 240 and the PA 203. Thecontroller 220 may cut off the electrical connection between the powerconverter 240 and the PA 203, and may control the power converter 240 soas to output power less than the existing output power.

When the detected supply current is less than or equal to the referencecurrent, the controller 220 may control the breaker 230 so as tomaintain the electrical connection between the power converter 240 andthe PA 203.

The breaker 230 may cut off the electrical connection between the powerconverter 240 and the PA 203 based on ON and OFF states of a switch. Thebreaker 230 may cut off the electrical connection between the powerconverter 240 and the PA 203 by an operation of a transistor. Whilecurrent output from the power converter 240 based on control of thecontroller 220 flows through the transistor, the breaker 230 may beconfigured to decrease the current by a predetermined value and mayprovide the decreased current to the PA 203.

A leakage current breaker 231 may cut off a leakage current so that thecurrent output from the power converter 240 is transferred to the PA 203without the leakage current. The leakage current breaker 231 may includea diode connection on a circuit in some embodiments.

FIG. 3 illustrates a wireless power transmitter.

Referring to FIG. 3, a detecting unit 310 may be configured to detect avoltage between both ends 311 and 313 of the transistor 340. Thetransistor 340 may include an ON resistor and thus, a voltage may beapplied between both ends 311 and 313 of the transistor 340. Thecontroller 320 may store information on the ON resistor of thetransistor 340.

The detecting unit 310 may be configured to detect a supply current Isbased on the detected voltage and the ON resistor of the transistor 340.For example, the transistor 340 may include various types oftransistors, such as, for example, a bipolar junction transistor (BJT),a field effect transistor (FET), an insulated gate bipolar transistor(IGBT), and the like. The supply current Is may be a current that thepower converter 240 generates and provides to the PA 203. The detectingunit 310 may provide, to controller 320, information on the detectedsupply current Is and the detected voltage.

The controller 320 may be configured to calculate a supply power basedon the detected voltage and the detected supply current Is. Thecontroller 320 may perform the calculation through a processor. Thecontroller 320 may determine a reference current matching the detectedvoltage and the calculated supply power, based on a reference table. Thecontroller 320 may transfer the reference to a comparing unit 330.

For example, the controller 320 may compare the determined referencecurrent and the detected supply current, and may control the powerconverter 240 so as to output an amount of power that is less than theexisting output power when the detected supply current is greater thanthe determined reference current.

The comparing unit 330 may compare the detected supply current and thereference current. In one or more embodiments, the comparing unit 330may output a “High” value or a “Low” value based on the comparison. Thetransistor 340 may be controlled based on the output value of thecomparing unit 330. For example, when the output value of the comparingunit 330 is the “High” value, the transistor 340 may cut off anelectrical connection between the power converter 240 and the PA 203.Conversely, when the output value of the comparing unit 330 is the “Low”value, the transistor 340 may maintain the electrical connection betweenthe power converter 240 and the PA 203.

Additionally, when the output value of the comparing unit 330 is the“High” value, the transistor 340 may maintain the electrical connectionbetween the power converter 240 and the PA 203. And, on the other hand,when the output value of the comparing unit 330 is the “Low” value, thetransistor 340 may maintain the electrical connection between the powerconverter 240 and the PA 203.

The operation of the transistor 340 controlled based on the output valueof the comparing unit 330 may be determined in advance or may bedetermined by a user.

A diode 350 may cut off a leakage current so that a current output fromthe power converter 240 and supplied to the PA 203 is prevented fromleaking. The diode 350 may be connected to a source and a drain of thetransistor 340 so as to cut off a leakage current component of thetransistor 340.

FIG. 4 illustrates a wireless power transmitter.

Referring to FIG. 4, a detecting unit 410 may be configured to detect avoltage applied between both ends 411 and 413 of a resistor Rs. Thecontroller 320 may store information on the resistor Rs.

The detecting unit 410 may detect a supply current, based on thedetected voltage and the resistor Rs. The supply current may be acurrent that the power converter 240 generates and provides to the PA203. The detecting unit 410 may provide, to the controller 420,information on the detected voltage and the detected supply current.

The controller 420 may calculate the supply power based on the detectedvoltage and the detected supply current. The controller 420 may performthe calculation through a processor. The controller 420 may determine areference current that matches the detected voltage and the calculatedsupply power, based on a reference table. The controller 420 may comparethe determined reference current and the detected supply current, andmay control an operation of a switch 430 based on a result of thecomparison. The switch 430 may include various types of switches, suchas, for example, a press button switch, a rotary switch, anelectromagnetic switch, a knife switch, a toggle switch, a rockerswitch, a slide switch, a touch switch, and the like.

The switch 430 may be configured to “cut off” or terminate an electricalconnection between the power converter 240 and the PA 203 based oncontrol of the controller 420. For example, when the detected supplycurrent is greater than the determined reference current, the controller420 may turn the switch 430 OFF so as to cut off the electricalconnection between the power converter 240 and the PA 203. Conversely,when the detected supply current is less than or equal to the referencecurrent, the controller 420 may turn the switch 4300N so as to maintainthe electrical connection between the power converter 240 and the PA203.

For example, the controller 420 may compare the determined referencecurrent and the detected supply current, and may control the powerconverter 240 to output an amount of power that is less than theexisting output power when the detected supply current is greater thanthe reference current. For example, when the power converter 240 outputsan amount of power that is less than the existing output power, thecontroller 430 may turn the switch 4300N so as to electrically connectthe power converter 240 and the PA 203.

The PA 203 may receive, from the power converter 240, a supply currentless than a limiting current and thus, may output power within a stableoutput range. And the PA 203 may output power without a momentaryoverpower so that a reliability of the wireless power transmitter mayincrease.

FIG. 5 illustrates a stable range of currents supplied to a PA.

The stable range of the currents supplied to the PA may be determinedbased on a requested power of a load of a target device. A number oftarget devices that are able to receive wireless power increases, anamount of the requested power of the load of the target device mayincrease. For example, when a requested power of a single terminal is 5W and another equivalent terminal is added, the requested power of theload of the target device may increase to 10 W. A limit of a supplycurrent of the PA may be determined based on an amount of an outputpower of the PA of the source device, for instance.

Referring to FIG. 5, when the requested power of the load of the targetdevice is 5 W, the stable range of the current supplied to the PA may be0.7 A. When the current supplied to the PA is greater than 0.7 A, the PAmay be damaged. Therefore, the supply current may be controlled so thatthe current supplied to the PA based on the requested power stays withinthe stable range. Even when the requested power of the load of thetarget device is 10 W or 20 W, the stable range of the current suppliedto the PA may be set.

FIG. 6 illustrates a reference table which may be used when a controllerof a wireless power transmitter determines a reference current. A supplyvoltage Vs of a PA, a supply power P, a reference current Ir may be setin the reference table. The controller may determine the referencecurrent based on the detected supply voltage Vs and the supply power P.For example, when the detected supply voltage Vs is 10 V and the supplypower P is 40 dBm, the reference current may be 1.1 A. The wirelesspower transmitter may be configured to compare the reference current anda detected supply current in order to control the supply power Psupplied to the PA.

In some instances, the values set in the reference table may be set by amanufacturer of a product in advance. Alternatively or additionally, thevalues set in the reference table may be collected or stored in adatabase by data collection of the wireless power transmitter.

FIGS. 7A and 7B illustrate distribution of a magnetic field in a feederand a source resonator.

When a source resonator receives power through a separate feeder,magnetic fields may be formed in both the feeder and the sourceresonator.

Referring to FIG. 7A, as an input current flows in a feeder 710, amagnetic field 730 may be formed. A direction 731 of the magnetic field730 within the feeder 710 may have a phase opposite to a phase of adirection 733 of the magnetic field 730 outside the feeder 710. Aninduced current may be formed in a source resonator 720 by the magneticfield 730 formed by the feeder 710. The direction of the induced currentmay be opposite to a direction of the input current.

Due to the induced current, a magnetic field 740 may be formed in thesource resonator 720. Directions of a magnetic field formed due to aninduced current in all positions of the source resonator 720 may beidentical. Accordingly, a direction 741 of the magnetic field 740 formedwithin the feeder 710 by the source resonator 720 may have the samephase as a direction 743 of the magnetic field 740 formed outside thefeeder 710 by the source resonator 720.

When the magnetic field 730 formed by the feeder 710 and the magneticfield 740 formed by the source resonator 720 are combined, strength ofthe total magnetic field may decrease within the feeder 710, but mayincrease outside the feeder 720. When power is supplied to the sourceresonator 720 through the feeder 710 configured as illustrated in FIG.7A, the strength of the total magnetic field may decrease in the centerof the source resonator 720, but may increase outside the sourceresonator 720. When a magnetic field is randomly distributed in thesource resonator 720, it may be difficult to perform impedance matching,since an input impedance may frequently vary. Additionally, when thestrength of the total magnetic field increases, the efficiency ofwireless power transmission may increase. Conversely, when the strengthof the total magnetic field is decreased, the efficiency of wirelesspower transmission may be reduced. Accordingly, the power transmissionefficiency may be reduced on average.

In a target resonator, a magnetic field may be distributed asillustrated in FIG. 7A. Current flowing in the source resonator 720 maybe induced by the input current flowing in the feeder 710 using amagnetic coupling between the source resonator 720 and the targetresonator. The current flowing in the target resonator may cause amagnetic field to be formed, so that an induced current may be generatedin a feeder located in the target resonator. Within the feeder, thedirection of a magnetic field formed by the target resonator may have aphase opposite to a phase of a direction of a magnetic field formed bythe feeder and accordingly, strength of the total magnetic field may bereduced.

FIG. 7B illustrates a structure of a wireless power transmitter in whicha source resonator 750 and a feeder 760 have a common ground. The sourceresonator 750 may include a capacitor 751. The feeder 760 may receive aninput of a radio frequency (RF) signal via a port 761.

For example, when the RF signal is input to the feeder 760, an inputcurrent may be generated in the feeder 760. The input current flowing inthe feeder 760 may cause a magnetic field to be formed, and a currentmay be induced in the source resonator 750 by the magnetic field.Additionally, another magnetic field may be formed due to the inducedcurrent flowing in the source resonator 750. A direction of the inputcurrent flowing in the feeder 760 may have a phase opposite to a phaseof a direction of the induced current flowing in the source resonator750. Accordingly, in a region between the source resonator 750 and thefeeder 760, a direction 771 of the magnetic field formed due to theinput current may have the same phase as a direction 773 of the magneticfield formed due to the induced current and thus, the strength of thetotal magnetic field may increase. Conversely, within the feeder 760, adirection 781 of the magnetic field formed due to the input current mayhave a phase opposite to a phase of a direction 783 of the magneticfield formed due to the induced current and thus, the strength of thetotal magnetic field may decrease. Therefore, the strength of the totalmagnetic field may decrease in the center of the source resonator 750,but may increase outside the source resonator 750.

The feeder 760 may be configured to determine an input impedance byadjusting an internal area of the feeder 760. The input impedance refersto an impedance viewed in a direction from the feeder 760 to the sourceresonator 750. When the internal area of the feeder 760 increases theinput impedance may also be increased. Conversely, when the internalarea of the feeder 760 is reduced, the input impedance may also bereduced.

Since the magnetic field is randomly distributed in the source resonator750 even when the input impedance is reduced, a value of the inputimpedance may vary depending on a location of a target device.Accordingly, a separate matching network may need to match the inputimpedance to an output impedance of a PA. For example, when the inputimpedance increases, a separate matching network may be used to matchthe increased input impedance to a relatively low output impedance.

As an example, when a target resonator has the same configuration as thesource resonator 750, and when a feeder of the target resonator has thesame configuration as the feeder 760, a separate matching network may beneeded, because a direction of a current flowing in the target resonatorhas a phase opposite to a phase of a direction of an induced currentflowing in the feeder of the target resonator.

FIG. 8A illustrates a wireless power transmitter.

Referring to FIG. 8A, the wireless power transmitter includes a sourceresonator 810, and a feeding unit 820. The source resonator 810 mayinclude a capacitor 811. The feeding unit 820 may be electricallyconnected to both ends of the capacitor 811.

FIG. 8B illustrates, in more detail, the structure of the wireless powertransmitter of FIG. 8A. The source resonator 810 includes a firsttransmission line, a first conductor 841, a second conductor 842, and atleast one first capacitor 850.

The first capacitor 850 may be inserted or otherwise positioned inseries between a first signal conducting portion 831 and a second signalconducting portion 832 in the first transmission line, and an electricfield may be confined within the first capacitor 850. For example, thefirst transmission line may include at least one conductor in an upperportion of the first transmission line, and may also include at leastone conductor in a lower portion of the first transmission line. Currentmay flow through the at least one conductor disposed in the upperportion of the first transmission line, and the at least one conductordisposed in the lower portion of the first transmission line may beelectrically grounded. For example, a conductor disposed in an upperportion of the first transmission line may be separated into and therebybe referred to as the first signal conducting portion 831 and the secondsignal conducting portion 832. A conductor disposed in a lower portionof the first transmission line may be referred to as a first groundconducting portion 833.

As illustrated in FIG. 8B, the source resonator 810 may have a generallytwo-dimensional (2D) structure. The first transmission line may includethe first signal conducting portion 831 and the second signal conductingportion 832 in the upper portion of the first transmission line. Inaddition, the first transmission line may include the first groundconducting portion 833 in the lower portion of the first transmissionline. The first signal conducting portion 831 and the second signalconducting portion 832 may be disposed to face the first groundconducting portion 833. Current may flow through the first signalconducting portion 831 and the second signal conducting portion 832.

Additionally, one end of the first signal conducting portion 831 may beelectrically connected (i.e., shorted) to the first conductor 841, andanother end of the first signal conducting portion 831 may be connectedto the first capacitor 850. One end of the second signal conductingportion 832 may be shorted to the second conductor 842, and another endof the second signal conducting portion 832 may be connected to thefirst capacitor 850. Accordingly, the first signal conducting portion831, the second signal conducting portion 832, the first groundconducting portion 833, and the conductors 841 and 842 may be connectedto each other, so that the source resonator 810 may have an electricallyclosed-loop structure. The term “closed-loop structure” as used herein,may include a polygonal structure, for example, a circular structure, arectangular structure, or the like that is a circuit that iselectrically closed.

The first capacitor 850 may be inserted into an intermediate portion ofthe first transmission line. For example, the first capacitor 850 may beinserted into a space between the first signal conducting portion 831and the second signal conducting portion 832. The first capacitor 850may be configured as a lumped element, a distributed element, or thelike. For example, a distributed capacitor having the shape of thedistributed element may include zigzagged conductor lines and adielectric material that has a high permittivity between the zigzaggedconductor lines.

When the first capacitor 850 is inserted into the first transmissionline, the source resonator 810 may have a characteristic of ametamaterial. The metamaterial indicates a material having apredetermined electrical property that has not been discovered innature, and thus, may have an artificially designed structure. Anelectromagnetic characteristic of the materials existing in nature mayhave a unique magnetic permeability or a unique permittivity. Mostmaterials may have a positive magnetic permeability or a positivepermittivity.

In the case of most materials, a right hand rule may be applied to anelectric field, a magnetic field, and a pointing vector, and thus, thecorresponding materials may be referred to as right handed materials(RHMs). However, the metamaterial that has a magnetic permeability or apermittivity absent in nature may be classified into an epsilon negative(ENG) material, a mu negative (MNG) material, a double negative (DNG)material, a negative refractive index (NRI) material, a left-handed (LH)material, and the like, based on a sign of the correspondingpermittivity or magnetic permeability.

When a capacitance of the first capacitor 850 inserted as the lumpedelement is appropriately determined, the source resonator 810 may havethe characteristic of the metamaterial. Because the source resonator 810may have a negative magnetic permeability by appropriately adjusting thecapacitance of the first capacitor 850, the source resonator 810 mayalso be referred to as an MNG resonator. Various criteria may be appliedto determine the capacitance of the first capacitor 850. For example,the various criteria may include a criterion for enabling the sourceresonator 810 to have the characteristic of the metamaterial, acriterion for enabling the source resonator 810 to have a negativemagnetic permeability in a target frequency, a criterion for enablingthe source resonator 810 to have a zeroth order resonance characteristicin the target frequency, and the like. Based on at least one criterionamong the aforementioned criteria, the capacitance of the firstcapacitor 850 may be determined.

The source resonator 810, also referred to as the MNG resonator 810, mayhave a zeroth order resonance characteristic (i.e., having, as aresonance frequency, a frequency when a propagation constant is “0”).Because the source resonator 810 may have a zeroth order resonancecharacteristic, the resonance frequency may be independent with respectto a physical size of the MNG resonator 810. By appropriately designingor configuring the first capacitor 850, the MNG resonator 810 maysufficiently change the resonance frequency. Accordingly, the physicalsize of the MNG resonator 810 may not be changed.

In a near field, for example, the electric field may be concentrated onthe first capacitor 850 inserted into the first transmission line.Accordingly, due to the first capacitor 850, the magnetic field maybecome dominant in the near field. The MNG resonator 810 may have arelatively high Q-factor using the first capacitor 850 of the lumpedelement, and thus, it may be possible to enhance an efficiency of powertransmission. For example, the Q-factor may indicate a level of an ohmicloss or a ratio of a reactance with respect to a resistance in thewireless power transmission. The efficiency of the wireless powertransmission may increase according to an increase in the Q-factor.

In one or more embodiments, a magnetic core may be further provided topass through the MNG resonator 810. The magnetic core may increase powertransmission distance.

Referring to FIG. 8B, the feeding unit 820 includes a secondtransmission line, a third conductor 871, a fourth conductor 872, afifth conductor 881, and a sixth conductor 882.

The second transmission line may include a third signal conductingportion 861 and a fourth signal conducting portion 862 in an upperportion of the second transmission line. In addition, the secondtransmission line may include a second ground conducting portion 863 ina lower portion of the second transmission line. The third signalconducting portion 861 and the fourth signal conducting portion 862 maybe disposed to face the second ground conducting portion 863, in someinstances. Current may flow through the third signal conducting portion861 and the fourth signal conducting portion 862.

Additionally, one end of the third signal conducting portion 861 may beshorted to the third conductor 871, and another end of the third signalconducting portion 861 may be connected to the fifth conductor 881. Oneend of the fourth signal conducting portion 862 may be shorted to thefourth conductor 872, and another end of the fourth signal conductingportion 862 may be connected to the sixth conductor 882. The fifthconductor 881 may be connected to the first signal conducting portion831, and the sixth conductor 882 may be connected to the second signalconducting portion 832. The fifth conductor 881 and the sixth conductor882 may be connected in parallel to both ends of the first capacitor850. Moreover, the fifth conductor 881 and the sixth conductor 882 maybe used as input ports to receive an input of an RF signal.

Accordingly, the third signal conducting portion 861, the fourth signalconducting portion 862, the second ground conducting portion 863, thethird conductor 871, the fourth conductor 872, the fifth conductor 881,the sixth conductor 882, and the source resonator 810 may be connectedto each other, so that the source resonator 810 and the feeding unit 820may have an electrically closed-loop structure. When an RF signal isreceived via the fifth conductor 881 or the sixth conductor 882, aninput current may flow in the feeding unit 820 and the source resonator810, a magnetic field may be formed due to the input current, and acurrent may be induced to the source resonator 810 by the formedmagnetic field. A direction of the input current flowing in the feedingunit 820 may be identical to a direction of the induced current flowingin the source resonator 810 and thus, strength of the total magneticfield may increase in the center of the source resonator 810, but maydecrease outside the source resonator 810. The direction of the inputcurrent, and the direction of the induced current will be furtherdescribed with reference to FIGS. 9A and 9B.

An input impedance may be determined based on an area of a regionbetween the source resonator 810 and the feeding unit 820 andaccordingly, a separate matching network used to match the inputimpedance to an output impedance of a PA may not be needed. For example,even when the matching network is used, the input impedance may bedetermined by adjusting the size of the feeding unit 820 and thus, astructure of the matching network may be simplified. The simplifiedstructure of the matching network may minimize a matching loss of thematching network.

The second transmission line, the third conductor 871, the fourthconductor 872, the fifth conductor 881, and the sixth conductor 882 mayform the same structure as the source resonator 810. When the sourceresonator 810 has a loop structure, the feeding unit 820 may also have aloop structure. And when the source resonator 810 has a circularstructure, the feeding unit 820 may also have a circular structure.

The above-described configuration of the source resonator 810 andconfiguration of the feeding unit 820 may be applied to the targetresonator and the feeding unit of the target resonator, respectively.When the feeding unit of the target resonator is configured as describedin the foregoing, the feeding unit may match an output impedance of thetarget resonator and an input impedance of the feeding unit, byadjusting a size of the feeding unit. Accordingly, a separate matchingnetwork may not be used.

FIG. 9A illustrates distribution of a magnetic field within a sourceresonator based on feeding of a feeding unit. Specifically, FIG. 9A morebriefly illustrates the source resonator 810 and the feeding unit 820 ofFIG. 8A. FIG. 9B illustrates one equivalent circuit of a feeding unit940, and an equivalent circuit of a source resonator 950.

A feeding operation may refer to supplying power to a source resonatorin a wireless power transmitter, or may refer to supplying AC power to arectifying unit in a wireless power receiver.

FIG. 9A illustrates a direction of an input current flowing in thefeeding unit, and a direction of an induced current induced in thesource resonator. Additionally, FIG. 9A illustrates a direction of amagnetic field formed due to the input current of the feeding unit, anda direction of a magnetic field formed due to the induced current of thesource resonator.

Referring to FIG. 9A, a fifth conductor or a sixth conductor of thefeeding unit may be used as an input port 910. The input port 910 mayreceive an input of an RF signal. The RF signal may be output from a PA.The PA may increase or decrease the amplitude of the RF signal, ondemand by a target device. The RF signal received by the input port 910may be displayed in the form of an input current flowing in the feedingunit. The input current may flow in a clockwise direction in the feedingunit, along a transmission line of the feeding unit. The fifth conductorof the feeding unit may be electrically connected to the sourceresonator, such as, for example, to a first signal conducting portion ofthe source resonator. Accordingly, the input current may flow in thesource resonator, as well as, in the feeding unit. The input current mayflow in a counterclockwise direction in the source resonator. The inputcurrent flowing in the source resonator may cause a magnetic field to beformed, so that an induced current may be generated in the sourceresonator due to the magnetic field. The induced current may flow in aclockwise direction in the source resonator. And the induced current maytransfer energy to a capacitor of the source resonator, and a magneticfield may be formed due to the induced current. The input currentflowing in the feeding unit and the source resonator may be indicated bya solid line of FIG. 9A, and the induced current flowing in the sourceresonator may be indicated by a dotted line of FIG. 9A.

A direction of a magnetic field formed due to a current may bedetermined based on the right hand rule. As illustrated in FIG. 9A,within the feeding unit, a direction 921 of a magnetic field formed dueto the input current flowing in the feeding unit may be identical to adirection 923 of a magnetic field formed due to the induced currentflowing in the source resonator. Accordingly, strength of the totalmagnetic field may increase within the feeding unit.

Additionally, in a region between the feeding unit and the sourceresonator, a direction 933 of a magnetic field formed dye to the inputcurrent flowing in the feeding unit has a phase opposite to a phase of adirection 931 of a magnetic field formed due to the induced currentflowing in the source resonator, as illustrated in FIG. 9A. Accordingly,strength of the total magnetic field may decrease in the region betweenthe feeding unit and the source resonator.

Generally, a strength of a magnetic field decreases in the center of asource resonator with the loop structure, and increases outside thesource resonator. However, referring to FIG. 9A, the feeding unit may beelectrically connected to both ends of a capacitor of the sourceresonator, and accordingly the induced current of the source resonatormay flow in the same direction as the input current of the feeding unit.Since the induced current of the source resonator flows in the samedirection as the input current of the feeding unit, the strength of thetotal magnetic field may increase within the feeding unit, and maydecrease outside the feeding unit. As a result, the strength of thetotal magnetic field may increase in the center of the source resonatorwith the loop structure, and may decrease outside the source resonator,due to the feeding unit. Thus, the strength of the total magnetic fieldmay be equalized within the source resonator. Additionally, the powertransmission efficiency for transferring a power from the sourceresonator to a target resonator may be in proportion to the strength ofthe total magnetic field formed in the source resonator. When thestrength of the total magnetic field increases in the center of thesource resonator, the power transmission efficiency may also increase.

FIG. 9B illustrates equivalent circuits of a feeding unit and a sourceresonator.

Referring to FIG. 9B, the feeding unit 940 and the source resonator 950may be expressed by the equivalent circuits. An input impedance Z_(in)viewed in a direction from the feeding unit 940 to the source resonator950 may be computed of determined using Equation 1.

$\begin{matrix}{Z_{in} = \frac{\left( {\omega \; M} \right)^{2}}{Z}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, M denotes a mutual inductance between the feeding unit940 and the source resonator 950, Ω denotes a resonance frequencybetween the feeding unit 940 and the source resonator 950, and Z denotesan impedance viewed in a direction from the source resonator 950 to atarget device. The input impedance Z_(in) may be in proportion to themutual inductance M. Accordingly, the input impedance Z_(in) may becontrolled by adjusting the mutual inductance M. The mutual inductance Mmay be adjusted based on an area of a region between the feeding unit940 and the source resonator 950. The area of the region between thefeeding unit 940 and the source resonator 950 may be adjusted based on asize of the feeding unit 940. The input impedance Z_(in) may bedetermined based on the size of the feeding unit 940 and thus, aseparate matching network may not need to perform impedance matchingwith an output impedance of a PA in some instances.

In a target resonator and a feeding unit included in a wireless powerreceiver, a magnetic field may be distributed as illustrated in FIG. 9A.For example, the target resonator may receive wireless power from asource resonator, using magnetic coupling. Due to the received wirelesspower, an induced current may be generated in the target resonator. Amagnetic field formed due to the induced current in the target resonatormay cause another induced current to be generated in the feeding unit.When the target resonator is connected to the feeding unit asillustrated in FIG. 9A, the induced current generated in the targetresonator may flow in the same direction as the induced currentgenerated in the feeding unit. Thus, strength of the total magneticfield may increase within the feeding unit, but may decrease in a regionbetween the feeding unit and the target resonator.

FIG. 10 illustrates an electric vehicle charging system.

Referring to FIG. 10, an electric vehicle charging system 1000 includesa source system 1010, a source resonator 1020, a target resonator 1030,a target system 1040, and an electric vehicle battery 1050.

The electric vehicle charging system 1000 may have a similar structureto the wireless power transmission system of FIG. 1. The source system1010 and the source resonator 1020 in the electric vehicle chargingsystem 1000 may function as a source. Additionally, the target resonator1030 and the target system 1040 in the electric vehicle charging system1000 may function as a target.

The source system 1010 may include an alternating current-to-directcurrent (AC/DC) converter, a power detector, a power converter, acontrol/communication unit, similarly to the source device of FIG. 1.The target system 1040 may include a rectification unit, a DC-to-DC(DC/DC) converter, a switch unit, a charging unit, and acontrol/communication unit, similarly to the target device 120 of FIG.1.

The electric vehicle battery 1050 may be charged by the target system1040.

The electric vehicle charging system 1000 may use a resonant frequencyin a band of a few kilohertz (KHz) to tens of MHz.

The source system 1010 may generate power, based on a type of chargingvehicle, a capacity of a battery, and a charging state of a battery, andmay supply the generated power to the target system 1040.

The source system 1010 may control the source resonator 1020 and thetarget resonator 1030 to be aligned. For example, when the sourceresonator 1020 and the target resonator 1030 are not aligned, thecontroller of the source system 1010 may transmit a message to thetarget system 1040, and may control alignment between the sourceresonator 1020 and the target resonator 1030.

For example, when the target resonator 1030 is not located in a positionenabling maximum magnetic resonance, the source resonator 1020 and thetarget resonator 1030 may not be aligned. When a vehicle does not stopaccurately, the source system 1010 may induce a position of the vehicleto be adjusted, and may control the source resonator 1020 and the targetresonator 1030 to be aligned.

The source system 1010 and the target system 1040 may transmit orreceive an ID of a vehicle, or may exchange various messages, throughcommunication.

The descriptions of FIGS. 2 through 9 may be applied to the electricvehicle charging system 1000. However, the electric vehicle chargingsystem 1000 may use a resonant frequency in a band of a few KHz to tensof MHz, and may transmit power that is equal to or higher than tens ofwatts to charge the electric vehicle battery 1050.

The units described herein may be implemented using hardware components,software components, or a combination thereof. For example, a processingdevice may be implemented using one or more general-purpose or specialpurpose computers, such as, for example, a processor, a controller andan arithmetic logic unit, a digital signal processor, a microcomputer, afield programmable array, a programmable logic unit, a microprocessor orany other device capable of responding to and executing instructions ina defined manner. The processing device may run an operating system (OS)and one or more software applications that run on the OS. The processingdevice also may access, store, manipulate, process, and create data inresponse to execution of the software. For purpose of simplicity, thedescription of a processing device is used as singular; however, oneskilled in the art will appreciated that a processing device may includemultiple processing elements and multiple types of processing elements.For example, a processing device may include multiple processors or aprocessor and a controller. In addition, different processingconfigurations are possible, such as parallel processors.

The software may include a computer program, a piece of code, aninstruction, or some combination thereof, for independently orcollectively instructing or configuring the processing device to operateas desired. Software and data may be embodied permanently or temporarilyin any type of machine, component, physical or virtual equipment,computer storage medium or device, or in a propagated signal wavecapable of providing instructions or data to or being interpreted by theprocessing device. The software also may be distributed over networkcoupled computer systems so that the software is stored and executed ina distributed fashion. In particular, the software and data may bestored by one or more computer readable recording mediums. The computerreadable recording medium may include any data storage device that canstore data which can be thereafter read by a computer system orprocessing device. Examples of the computer readable recording mediuminclude read-only memory (ROM), random-access memory (RAM), CD-ROMs,magnetic tapes, floppy disks, optical data storage devices. Also,functional programs, codes, and code segments for accomplishing theexample embodiments disclosed herein can be easily construed byprogrammers skilled in the art to which the embodiments pertain based onand using the flow diagrams and block diagrams of the figures and theircorresponding descriptions as provided herein.

A number of example embodiments have been described above. Nevertheless,it should be understood that various modifications may be made. Forexample, suitable results may be achieved if the described techniquesare performed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

1. A power supply for a wireless power transmitter comprising: a detecting unit configured to detect voltage, current, or both supplied to a power amplifier (PA); a controller configured to determine power supplied to the PA based on the detected voltage, the detected current, or both, and to determine a reference current based on the determined power supplied to the PA; and a breaker configured to cut off the power supplied to the PA based on a comparison of current supplied to the PA and the reference current.
 2. The power supply of claim 1, wherein the detecting unit measures voltage across a resistor or a transistor connected to the PA, measures current flowing through the resistor or the transistor, or both.
 3. The power supply of claim 1, wherein the detecting unit measures voltage across a resistor having a predetermined resistance connected to the PA, and determines the current based on the predetermined resistance and the measured voltage.
 4. The power supply of claim 1, wherein the controller determines the reference current using a reference table in which reference currents, predetermined supply powers, and supply voltages, are provided.
 5. The power supply of claim 1, wherein the controller controls a signal input to the PA based on the comparison.
 6. The power supply of claim 1, wherein the controller controls power output from a power converter that provides supply power to the PA based on the comparison.
 7. The power supply of claim 1, further comprising: a comparing unit configured to compare current supplied to the PA and the reference current.
 8. The power supply of claim 1, wherein the breaker determines the state of a switch that connects the PA and a power converter based on the comparison.
 9. The power supply of claim 1, wherein the breaker determines an operation of a transistor that connects the PA and a power converter based on the comparison.
 10. The power supply of claim 1, further comprising: a leakage current breaker configured to cut off a leakage current.
 11. The power supply of claim 1, further comprising: a source resonance unit configured to transmit power output from the PA; and a matching network configured to match an output impedance of the PA and an input impedance of the source resonator.
 12. A power supply method for wireless power transmission, the method comprising: detecting voltage, current, or both, supplied to a power amplifier (PA); determining power supplied to the PA based on the detected voltage, the detected current, or both; determining a reference current based on the determined power supplied to the PA; and cutting off the power supplied to the PA based on comparison of current supplied to the PA and the reference current.
 13. The method of claim 12, wherein the detecting comprises: measuring voltage across a resistor or a transistor connected to the PA, measuring current flowing through the resistor or the transistor, or both.
 14. The method of claim 12, wherein the detecting comprises: measuring voltage across a resistor having a predetermined resistance connected to the PA; and determining the supply current based on the predetermined resistance and the measured voltage.
 15. The method of claim 12, further comprising: controlling power output from a power converter that provides power to the PA based on the comparison.
 16. The method of claim 12, further comprising: comparing the detected supply current and the reference current.
 17. The method of claim 12, wherein the cutting off comprises: cutting off an electrical connection between the PA and the power converter based on the comparison.
 18. A wireless power transmitter comprising the power supply of claim
 1. 